Keep Your U-50 Measuring Accurately with Genuine HORIBA Parts
The HORIBA U-50 series is one of the most widely used multiparameter water quality meters in Australia, trusted across environmental monitoring, water treatment, aquaculture, and industrial process control. To maintain measurement accuracy and extend instrument life, using genuine HORIBA U-50 accessories is essential.
This guide covers every replacement part, consumable, and accessory available for the U-50 series — including when to replace each component, proper maintenance procedures, and how each accessory contributes to reliable field measurements.
All accessories listed below are available from Australian Scientific, the authorised Australian distributor of HORIBA water quality instruments, with same-day dispatch on stocked items for orders placed by 1 pm AEST.
pH Measurement Accessories
Accurate pH measurement on the HORIBA U-50 relies on two electrodes working in tandem: the pH glass electrode and the pH reference electrode. Both require periodic replacement and ongoing maintenance to ensure consistent, reliable readings in the field.
pH Glass Electrode #7112
The pH glass electrode (sensor #7112) is the primary sensing element for pH measurement on the U-50. It generates a voltage proportional to the hydrogen ion activity in the sample, which the meter interprets as a pH value. This electrode works in conjunction with the pH reference electrode #7210 to provide a complete measurement circuit.
Expected lifespan: Approximately 2–3 years under normal operating conditions. The lifespan will be significantly reduced if correct care and maintenance procedures are not followed. Factors such as exposure to high-temperature samples, strongly acidic or alkaline solutions, and prolonged dry storage can all accelerate electrode degradation.
pH Protection Cap (Black)
The black pH protection cap is supplied with the pH glass electrode and must cover the sensor whenever the meter is not in use. A few drops of water should be placed inside the cap to keep the glass bulb hydrated. If the glass membrane dries out, sensor performance will deteriorate and response times will become noticeably slower. Replacement caps are available in packs of three.
pH Reference Electrode #7210
The pH reference electrode (#7210) provides the stable, constant electrical potential required for accurate pH measurement. Without a reliable reference, it is impossible to measure the voltage difference needed to determine hydrogen ion activity in a water sample. This electrode is also used as the reference for ORP measurements.
Expected lifespan: Approximately 4 years under normal conditions.
pH Reference Liquid Junction Cap
The liquid junction cap fits on the pH reference electrode #7210 and should be replaced if the wick becomes shortened or clogged. A compromised liquid junction can cause unstable or drifting pH readings, so periodic inspection of this component is an important part of routine maintenance.
pH KCl Reference Filling Solution
This potassium chloride (KCl) solution is used to refill the pH reference electrode #7210. To refill, simply remove the liquid junction cap and replenish the solution. The filling solution should be replaced every 2–3 months, or more frequently depending on usage intensity.
Important: If the meter has been stored for an extended period, always check whether the reference filling solution has solidified. If crystallisation has occurred, rinse the electrode cavity with fresh water and refill with new solution before use.
For a detailed maintenance walkthrough, refer to our article: pH Maintenance for HORIBA U-50 Water Quality Meter
ORP Measurement Accessories
ORP Electrode #7313
The ORP (oxidation-reduction potential) electrode #7313 measures the oxidising or reducing capacity of a water sample. It operates in conjunction with the pH reference electrode #7210, which provides the stable reference potential needed for ORP determination.
Expected lifespan: Approximately 5 years or more under normal operating conditions, making it one of the most durable sensors on the U-50 probe.
Dissolved Oxygen (DO) Measurement Accessories
The dissolved oxygen sensor on the HORIBA U-50 uses a polarographic measurement principle and requires regular consumable replacement to maintain accuracy. This section covers all DO-related accessories and their maintenance intervals.
Dissolved Oxygen Electrode #7543
The DO electrode (#7543) is a polarographic-type sensor used for measuring dissolved oxygen concentration in water. It requires a minimum 15-minute warm-up period before calibration or measurement to allow the electrode to polarise and stabilise.
Periodic maintenance is required every 3–6 months, which involves replacing both the DO membrane cap and the DO filling solution. Neglecting this maintenance schedule can result in sluggish response, inaccurate readings, or complete sensor failure.
For a detailed step-by-step maintenance guide, visit: Dissolved Oxygen Sensor Maintenance Guide – HORIBA U-50 Series
Dissolved Oxygen Membrane Cap
The DO membrane cap should be replaced every 3–6 months as part of routine maintenance. The membrane allows oxygen to diffuse through to the electrode while preventing other substances from reaching the sensor surface. Over time, the membrane can become fouled, stretched, or damaged, leading to measurement errors.
There is a specific procedure for replacing the membrane cap correctly. Improper installation can trap air bubbles beneath the membrane, which will cause inaccurate readings. Contact Australian Scientific for detailed replacement instructions.
Dissolved Oxygen Reference Filling Solution #306
This electrolyte solution is used to fill the DO membrane cap each time it is replaced. The filling solution is essential for the electrochemical reaction that enables dissolved oxygen measurement. Fresh solution must be used each time the membrane cap is changed.
Dissolved Oxygen Protection Cap (White)
The white DO protection cap is supplied with the dissolved oxygen electrode and must be fitted whenever the meter is not in use. Place a few drops of water inside the cap to prevent the membrane from drying out, which can slow response time and shorten membrane life. Replacement caps are available in packs of three.
Turbidity Measurement Accessories
Turbidity Sponge Brush
The turbidity sensor on the U-50 requires regular cleaning to maintain measurement accuracy. HORIBA supplies a dedicated sponge brush designed to clean the sensor window without causing scratches or damage.
Recommended cleaning procedure:
| Step | Method |
|---|---|
| Cleaning frequency | Every 2 months, or more often when measuring samples with high suspended solids |
| Method 1 | Use the sponge brush with a mild detergent solution (a few drops of dishwashing liquid in 500 ml of lukewarm water) |
| Method 2 | Wet both the probe and the sponge brush, apply a drop of dishwashing liquid directly to the brush, pass it through the turbidity sensor opening several times, then rinse thoroughly with clean water |
Calibration Accessories
Calibration Beaker Set
The calibration beaker set consists of a black outer container and a clear inner insert, designed specifically for calibrating the U-50 series with calibration solutions.
The clear insert features a slot that holds the dissolved oxygen electrode in air during calibration, preventing contact with the liquid calibration solution. For two-point dissolved oxygen calibration (using zero oxygen solution), the inner insert must be removed so the DO sensor can be fully immersed in the black outer container.
Auto Calibration Solution (100-4 / pH 4)
The U-50 series supports automatic single-point calibration using the HORIBA Auto Calibration Solution (also referred to as pH 4 or 100-4) in conjunction with the calibration beaker set. AUTO mode calibrates the following parameters simultaneously:
| Parameter | Calibration Point |
|---|---|
| pH | pH 4.00 |
| Conductivity | 4.49 mS/cm at 25°C |
| Turbidity | Zero (0 NTU) |
| Dissolved Oxygen | Span (air calibration) |
***Auto calibration is not possible with a normal colour-coded red pH 4.00 buffer solution.***
Only the HORIBA-specific Auto Calibration Solution (100-4) is compatible with the AUTO calibration function. For more precise calibration, manual multi-point calibration is recommended. Contact Australian Scientific for detailed calibration documentation.
HORIBA U-50 Accessories – Maintenance Schedule at a Glance
The table below summarises the approximate key replacement intervals for all major U-50 consumables and accessories if proper storage and maintenance is maintained. Adhering to this schedule helps ensure reliable measurements and extends the overall life of the instrument.
| Accessory | Replacement Interval | Key Note |
|---|---|---|
| pH Glass Electrode #7112 | 2–3 years | Store with hydrated cap |
| pH Reference Electrode #7210 | ~4 years | Check for solidified filling solution |
| pH Reference Filling Solution | Every 2–3 months | Replace more often with heavy use |
| pH Liquid Junction Cap | As needed | Replace if wick shortens or clogs |
| ORP Electrode #7313 | 5+ years | Uses pH reference #7210 |
| DO Electrode #7543 | Sensor-dependent | 15-min warm-up required |
| DO Membrane Cap | Every 3–6 months | Follow proper replacement procedure |
| DO Filling Solution #306 | With each membrane change | Use fresh solution only |
| Turbidity Sponge Brush | Cleaning every 2 months | More often for dirty samples |
| Auto Cal Solution (100-4) | As needed | Not compatible with standard pH 4 buffer |
Where to Buy HORIBA U-50 Accessories in Australia
Australian Scientific is the authorised Australian distributor for HORIBA water quality instruments and accessories. We provide:
- Genuine HORIBA U-50 replacement parts, electrodes, and consumables
- Full range of calibration solutions
- Technical support and maintenance advice
- Same-day dispatch across Australia on stocked items
- Servicing and repair for the HORIBA U-50 series
Need parts or have a technical question?
Contact Australian Scientific Browse U-50 Accessories
Phone: 1800 021 083 | Email: sales@austscientific.com.au